Thermally actuated valve assembly

ABSTRACT

A thermally actuated valve assembly especially adapted for use as a pilot valve for opening a fire extinguishing sprinkler in response to sensing a predetermined elevated ambient temperature level. The pilot valve assembly is removably installable as a unit in the main valve which has a passage therein constituting a portion of an auxiliary flow path. This passage has an inlet, an outlet, and a valve seat therebetween. A valve member is movable between a closed position in engagement with the valve seat for blocking the flow of water therethrough and an open position clear of the valve seat in which opening of the sprinkler is effected. A spring biases the valve member toward its closed position. A thermostatic disk is carried by the pilot valve and is interconnected with its valve member. The disk is responsive to ambient air temperature to abruptly move over center from a first curvature position to a second curvature position when subjected to a predetermined elevated ambient temperature level. The valve assembly also includes abutment means spaced from the disk when the latter is in its first curvature position but engageable by the disk as it moves over center from its first to its second curvature position. This permits free movement of the disk until it engages the abutment means without application of force to the valve member. Upon engagement of the disk with the abutment means the disk applies a force to the valve member to move it against the force of the spring biasing the valve member toward its closed position.

United States Patent Doherty, Jr.

[ Nov. 19, 1974 THERMALLY ACTUATED VALVE ASSEMBLY [75] Inventor: John Doherty, Jr-, Assonet, Mass.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: Dec. 26, 1973 [21] Appl. No.: 428,600

[52] US. Cl. 169/37, 169/90 [51] Int. Cl. A62c 37/08 [58] Field of Search 169/37, 90, 56, 60, 19; 137/457 [56] References Cited UNITED STATES PATENTS 1,913,035 6/1933 Loepsinger 169/37 3,757,866 9/1973 Mears et al. 169/37 Primary Examiner-M. Henson Wood, Jr. Assistant ExaminerMichael Mar Attorney, Agent, or Firm-John A. Haug; James P. McAndrews; Edward J. Connors, Jr.

[57] ABSTRACT A thermally actuated valve assembly especially adapted for use as a pilot valve for opening a fire extinguishing sprinkler in response to sensing a predetermined elevated ambient temperature level. The pilot valve assembly is removably installable as a unit in the main valve which has a passage therein constituting a portion of an auxiliary flow path. This passage has an inlet, an outlet, and a valve seat therebetween. A valve member is movable between a closed position in engagement with the valve seat for blocking the flow of water therethrough and an open position clear of the valve seat in which opening of the sprinkler is effected. A spring biases the valve member toward its closed position. A thermostatic disk is carried by the pilot valve and is interconnected with its valve member. The disk is responsive to ambient air temperature to abruptly move over center from a first curvature position to a second curvature position when sub jected to a predetermined elevated ambient temperature level. The valve assembly also includes abutment means spaced from the disk when the latter is in its first curvature position but engageable by the disk as it moves over center from its first to its second curvature position. This permits free movement of the disk until it engages the abutment means without application of force to the valve member. Upon engagement of the disk with the abutment means the disk applies a force to the valve member to move it against the force of the spring biasing the valve member toward its closed position.

6 Claims, 3 Drawing Figures 1 THERMALLY ACTUATED VALVE ASSEMBLY BACKGROUND OF THE INVENTION This invention relates to a thermally actuated valve assembly and more particularly to a pilot valve assembly adapted to sense ambient air temperature and to actuate a main valve, such as a sprinkler valve, upon sensing a predetermined elevated ambient temperature level.

Sprinkler systems have long been used in commercial and industrial buildings for fire fighting purposes. Typically, these sprinkler valves are held closed by means of a thermal fuse which when heated to a predetermined elevated temperature level opens the main sprinkler valve. Upon opening, the sprinkler valve remains open until the water supply is shut off remotely and a new thermal fuse is installed to hold the sprinkler valve closed.

On other sprinkler valves, such as disclosed in US. Pat. No. 3,698,483, sprinkler valves automatically reclose after the ambient temperature level is reduced below a predetermined level thus indicating that the fire has been extinguished. This automatic closing of the sprinkler valve prevents excessive water damage to the contents in the room. Generally, these automatically resettable sprinkler valves utilize a reversible thermal actuator, e.g., an expansible piston actuator operable by a change in state of a material such as a wax which melts at a known temperature and undergoes a relatively large change in volume. Thermostatic disks have also been used as thermal actuators to actuate a pilot valve which in turn controls operation of a resettable sprinkler valve. These reclosable sprinkler valves should not only reliably open at a predetermined elevated ambient temperature level (e.g., 165F.), but must not reclose until the ambient temperature has fallen below a second lower ambient temperature level (this second lower temperature indicating that the fire has been extinguished).

The prior automatically reclosable sprinkler valves have not, however, been wholly satisfactory. For example, some have been difficult to conveniently adjust or calibrate to insure that they will reliably and accurately open and reclose at temperatures within the necessary close tolerances. Others have relied on the force exerted by the thermostatic actuator to maintain the pilot valve closed so that there was leakage at higher normal ambient temperatures and/or under higher water pressures.

SUMIVIARY OF THE INVENTION Among the several objects of this invention may be noted the provision of a thermally actuated valve assembly useful for directly controlling relatively low flow rates of a fluid or useful as a pilot valve for opening the main valve of a high flow rate valve assembly, such as a fire extinguishing sprinkler, upon sensing a predetermined elevated ambient temperature level; the provision of such a valve assembly in which its thermal actuator is unloaded except upon instantaneous operation thereof and is not subject to leakage at higher normal ambient temperatures and/or higher fluid pressures; the provision of such a valve assembly in which its thermal actuator may be conveniently calibrated or adjusted to open and close either when installed in a main valve assembly or prior to installation in the main valve assembly; the provision of such a valve assembly in which operation thereof is substantially independent of fluid pressure in the valve assembly; the provision of such a valve assembly which will reliably reclose upon ambient temperature dropping below a specified temperature; and the provision of such a valve assembly which is of relatively economical construction and which is reliable in operation.

Briefly, a thermally actuated valve assembly of this invention is installed as a unit in a fluid flow path, e.g., in an auxiliary passage in the body of a main valve, such as a fire extinguishing sprinkler valve. It comprises a housing having a passage therein constituting a portion of the fluid flow path. The passage has an inlet and an outlet, and has a valve seat between the inlet and said outlet. A valve member in the valve housing is movable between a closed position inengagement with the valve seat for blocking the flow of fluid therethrough and an open position clear of the valve seat. A spring biases the valve member toward its closed position. A thermostatic disk responsive to ambient air temperature interconnects the disk and the valve member. The disk is movable over center from a first curvature position to a second curvature position when subjected to a predetermined elevated temperature level. Abutment means carried by the housing are spaced from the disk when the latter is in its first curvature position and are engageable by the disk as it moves from its first to its second curvature position thereby to permitfree movement of the disk until it engages the abutment means without application of force to the valve member. Upon engagement of the disk with the abutment means a force is applied to the valve member to move it against the force of the spring toward its open position.

Other objects and features of the invention will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical section of a sprinkler valve assembly having a main valve member shown in its closed position and a thermally actuated pilot valve assembly of this invention installed therein for controlling operation of the sprinkler valve, with the pilot valve assembly shown in its closed position;

FIG. 2 is a view similar to FIG. 1 illustrating the main valve of the sprinkler valve and the pilot valve in their respective open positions; and

FIG. 3 is an enlarged longitudinal cross section of the pilot valve assembly in its closed position.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, a sprinkler valve assembly (also referred to as a main valve assembly), is indicated in its entirety at l, and a thermally actuated pilot valve assembly of this invention is indicated in its entirety at 3. Briefly, the sprinkler valve assembly includes a sprinkler valve body 5 having a main passage 7 therethrough, through which a relatively high flow rate of water may flow, with one end of this main passage constituting an inlet 9 and the other end constituting an outlet 11. Inlet end 9 of the valve body is threaded, as indicated at 13, for connection to a pressurized water line and the outlet end is adapted to spray water in a predetermined pattern, a spray deflector 15 being provided for this purpose. The housing has a main valve seat 17 between its inlet and outlet ends and a main valve member 19 is movable between a closed position (see FIG. 1) in which it is in sealing engagement with valve seat 17 thereby to prevent the flow or leakage of water past the valve seat and an open position (see FIG. 2) permitting the flow of water through the main passage.

More particularly, valve body has a valve chamber 21 therein for reception of main valve member 19, the latter constituting a piston movable axially within the chamber between its closed and open positions. Main valve member 19 has a valve seal or O-ring 23 engageable with valve seat 16 thereto to seal main passage 7 and a body seal 25 surrounding its body for sealing it relative to the side walls of chamber 21. The main valve member has a first pressure area, generally corresponding to its cross sectional area at O-ring seal 23, against which water pressure from the water line acts to move the valve from its closed position toward its open position, and a second pressure area, corresponding generally to the area of its face 27, against which water pressure from the water line acts to seat the main valve member against its valve seat 17 so as to maintain the main valve member closed against the force exerted by water pressure acting against the first pressure area. A coil spring 23 biases valve member 19 toward its closed position.

An auxiliary passage, as indicated at 31, is provided in main valve member 19 and in body 5 so that water pressure may be equalized between the first and second pressure areas of the main valve member and so that water pressure may be selectively vented from the second pressure area to permit opening of the main valve member. This passage has an orifice 32 of relatively small cross section and thus restricts high flow rates of water from entering chamber 21. Specifically, this auxiliary passage includes an opening 33 in main valve member 17 to admit water under pressure from inlet end 9 of main passage 7 into chamber 21 and a passage 35 from chamber 21 to a vent port 37 opening into main passage 7 downstream from valve seat 17. A strainer 39 in valve member 19 prevents foreign particles from entering chamber 21.

In accordance with this invention, thermally actuated pilot valve assembly 3 is removably insertable as a unit into sprinkler valve body 5 in communication with auxiliary passage 31, and more specifically is insertable into passage 35 between the second pressure area of main valve member 19 (or chamber 21) and vent port 37. The pilot valve assembly includes a valve housing 39, the inner end portion 41 of which, when installed in sprinkler valve housing 5, blocks vent port 37 and blocks communication between chamber 21 and the vent port. The pilot valve housing has a passage 43 therein extending through end portion 41 thereof. This passage constitutes a portion of auxiliary passage 31 when the pilot valve is installed in sprinkler valve housing 5, and has an inlet opening 45in communication with passage 35 and an outlet 47 in communication with vent port 37. Passage 43 has a pilot valve seat 49 therein between inlet 45 and outlet 47 and a pilot valve member 51 movable therein between a closed position (as shown in FIGS. 1 and 3) and an open position (as shown in FIG. 2). With the pilot valve member 51 in its closed position, water pressure is maintained in auxiliary passage 35 so as to exert a force on the face 27 of the main valve member sufficient to maintain the valve member in its closed position against the force of water pressure acting against the first pressure area thereof.

' With the pilot valve member in its open position, water from within auxiliary passage 33 is vented thereby re ducing the water pressure acting against face 27 of the main valve member so as to enable the water pressure acting against the first pressure area to open the main valve member.

As previously mentioned, pilot valve assembly 3 is a thermally actuated valve and includes a thermostatic bimetal dish-shaped disk 53 (i.e., a thermal actuator). This disk is abruptly movable over center from a first curvature position (as shown in FIGS. 1 and 3) to a second or reversed curvature position (as shown in FIG. 2) when subjected to a predetermined elevated ambient temperature level (e.g., F.) which is indicative that a fire is burning nearby, this temperature being referred to as the actuation or trip temperature of the disk. As indicated at 55, means are provided in pilot valve 3 for interconnecting pilot valve 51 and disk 53. Housing 39 has abutment means 56 spaced from the disk when the latter is in its first curvature position but which are engageable by the disk as it snaps over center to its second curvature position thereby to permit free movement of the disk until it engages the abutment means without application of force to pilot valve member 51 and upon the disk snapping over center applying a force to the pilot valve to effect opening thereof and of sprinkler valve 1. This free movement or lost motion of the disk permits flexing of the disk (i.e., creep) without exerting a force on the pilot valve member 51 and prevents leakage at high ambient temperatures below the trip temperature of the disk. It will also be noted that the disk is unloaded prior to overcentering. Disk 53 is also reversibly movable from its second curvature position to its first curvature position upon ambient room temperature dropping below another predetermined temperature (referred to as its reset temperature) lower than its trip temperature so as to move pilot valve 51 from its open to its closed position and thus automatically close sprinkler valve 1.

More particularly, pilot valve housing 39 has an axial bore 57 extending therethrough from passage 43 exteriorly of the housing. The exterior of the housing is threaded, as indicated at 59, for removable insertion into a threaded opening 60 in sprinkler valve body 5. The valve housing carries O-ring seals 61 engageable with the sprinkler valve body 5 for sealing the pilot valve housing relative to the sprinkler valve body. As indicated at 62 in FIG. 3, end portion 41 of pilot valve housing 39 is adapted to sealingly engage O-ring 63 in sprinkler valve body 5 surrounding vent 37 so as to seal the pilot valve housing relative to auxiliary passage 31.

Interconnecting means 55 includes a rod 67 secured to pilot valve 51 and extending axially through bore 57 exteriorly of housing 39 and carrying disk 53. Glands or bushings 69a, 69b within bore 57 serve as guides for rod 67 and permit axial movement thereof. A packing seal 71 between glands 69a, 69b prevents leakage through bore 57 and yet permits axial movement of the rod. Pilot valve 51 includes a head 73 secured to the inner end of rod 67 and a resilient valve member of a suitable synthetic or natural elastomer or the like. A

compression coil spring 77 surrounds rod 67 and is in terposed between gland 69a and head 73 so as to bias pilot valve 51 toward its closed position. The force exerted by the spring on pilot valve 51 is established by accurately gaging the distance between the inner face of bushing 69a and the back face of head 73 so as to precompress spring 77 a desired amount to exert a predetermined closing force on the pilot valve 1.

The force of spring 77 closes the pilot valve and establishes a seal. The fluid pressure acting against the head 73 then maintains sealing force sufficient for the pressure applied. It will be noted that coil spring 77 can thus be made with a force and spring rate low enough that it will have minimal influence on the reset temperature. As indicated at 79, the outer end of rod 67 is threaded and a nut 81 adapted to support disk 53 is threaded thereon. More particularly, nut 81 extends through a central hole 83 in disk 53. A spring clip 85 is installed on nut 81 to hold the disk captive on the nut, but does not let it interfere with movement of the disk. A look nut 86 prevents movement of nut 81 along threaded portion 79. A shroud, generally indicated at 87, constitutes the outer end of housing 39. Shroud 87 is generally circular in cross section and includes a shoulder 89 of somewhat smaller diameter than disk 53. As best shown in FIG. 3, disk 53 is partially housed within shroud 87 and the shroud is open so that room air may freely circulate about the disk thereby to insure that the disk is responsive to room air temperature. Shoulder 89 constitutes abutment means 56 against which the outer margins of the disk may react as it snaps over center from its first curvature position to its second curvature position so as to enable the disk to exert a force on rod 67 sufficient to move pilot valve member 51 from its closed to its open position.

It will be noted that with disk 53in its first curvature position (as shown in FIGS. 1 and 3) and with pilot valve 51 closed, the diskis spaced from shoulder 89. Upon the disk being exposed to an ambient temperature level above its trip temperature, the disk will flex from its first curvature position towards a neutral position (not shown) between its first and second curvature positions. The disk is preferably spaced from shoulder 89 so it will contact the shoulder approximately as it moves past its neutral position. The distance the disk is spaced from shoulder 89 permits initial flexing of the disk at temperatures below its trip temperature without applying any force to rod 67 because there is no reaction point for the disk. However, with the disk in contact with shoulder 89, the disk exerts a sufficient force on rod 67 to overcome the force of spring 77 to open pilot valve 51. Thus, with the disk at temperatures below its trip temperature and out of engagement with abutment shoulder 89, the full force of spring 77 is exerted on pilot valve 51 to maintain it seated on its valve seat 49. This substantially avoids any leakage of the pilot valve due to fluctuating ambient temperatures and also insures that the pilot valve remain seated regardless of water pressure in auxiliary passage 31.

It will be understood that the temperature at which the disk snaps over center from its second to its first curvature position (i.e., its reset temperature) is affected by the force exerted on the periphery of the disk by shoulder 89 when the disk is in its second position. Thus, nut 81 may be adjusted along threaded portion 79 or rod 67 to vary the force exerted on the disk by abutment shoulder 89 to thus adjust or calibrate the disk to remain in its second curvature position at temwith the pilot valve assembly removed from sprinkler' valve assembly 1. This is particularly advantageous because the pilot valve assembly may be precalibrated at the factory and then field-installed in the sprinkler valve housing. Of course, it will be understood that the pilot valve assembly may be calibrated while installed in the sprinkler valve assembly.

It will also be understood that valve assembly 3, in addition to being useful as a pilot valve for controlling the relatively high rate of a main valve, such as a fire extinguishing sprinkler, may also be used to directly control the flow of any fluid in response to predetermined temperature conditions.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a main valve assembly, such as for a fire extinguishing sprinkler, having a valve body with a main passage therethrough, one end of said main passage constituting an inlet adapted for connection to a pressurized fluid source and the other end thereof constituting an outlet adapted for the discharge of fluid, a main valve seat in said main passage between said inlet and said outlet, valve means movable between a closed position in engagement with said main valve seat blocking communication between said inlet and said outlet and an open position permitting the flow of fluid through said main passage, said main valve means having a first pressure area against which fluid pressure acts to move said valve means from its closed position to its openposition and a second pressure area larger than the first pressure area against which fluid pressure acts to seat said valve means against said main valve seat so as to maintain said main valve means in its closed position against the force exerted by fluid pressure acting against said first pressure area, an auxiliary passage between said first pressure area and said second pressure area for equalizing fluid pressure applied to the first and second pressure areas, said auxiliary passage including a vent for venting fluid pressure from acting against said second pressure area; a thermally actuated pilot valve assembly for effecting opening of said main valve assembly in response to being subjected to a predetermined elevated ambient temperature, said pilot valve comprising a housing removably insertable as a unit into said valve body in said auxiliary passage between said second pressure area and said vent, a pilot valve passage in said valve housing consituting a portion of said auxiliary passage through which all fluid vented from said vent port must flow, said pilot valve passage having an inlet,

an outlet and a valve seat therebetween, said pilot valve assembly further comprising a pilot valve member movable in said pilot valve housing between a closed position in which said pilot valve member is seated in said pilot valve thereby to block communication between said second pressure area in said vent so as to maintain fluid pressure acting against said second pressure area and to maintain said main valve means in its closed position and an open position for venting fluid pressure from said auxiliary passage thus reducing the fluid pressure acting against the second pressure area so as to enable fluid pressure acting against the first pressure area to open said main valve means, means for biasing said pilot valve towards its closed position, a thermostatic disk carried by said pilot valve housing, said disk being abruptly movable over center from a first curvature position to a second curvature position when subjected to said predetermined ambient temperature, means interconnecting said disk and said pilot valve member, and abutment means spaced from said disk when the latter is in its first curvature position and engageable by said disk as it moves from its first to its second curvature position thereby to permit free movement of said disk until it engages said abutment means without application of force to said pilot valve member and, upon engagement of the disk by said abutment means, to apply a force to said pilot valve member via said interconnecting means so as to move it against the force of said biasing means toward its open position.

2. In a main valve assembly as set forth in claim 1 wherein said disk is reversibly movable from its second to its first curvature position upon its temperature falling below a second temperature less than said first predetermined temperature, said interconnecting means including means mounting said disk for varying the position of said disk relative to said abutment means whereby the disk may be calibrated to move from its second to its first curvature position at a preselected second temperature.

3. In a main valve assembly as set forth in claim 1 wherein said interconnecting means is a rod interconnecting said disk in said pilot valve member, and wherein said biasing means includes a compression spring biasing said pilot valve member into engagement with its respective said valve seat.

4. In a main valve assembly as set forth'in claim 3 wherein said rod has a threaded portion at its outer end, and said interconnecting means comprises a nut adjustable on said threaded portion, said disk being carried by said nut so as to permit the disk to move freely between its first and second curvature positions, said disk being positioned on said rod so that said disk is clear of said abutment means when said pilot valve member is closed, and said disk is engageable with said abutment means only as said disk abruptly moves from its first to its second curvature position thereby to maintain said pilot valve member closed until said disk moves from its first to its second curvature position.

5. In a sprinkler valve assembly as set forth in claim 4 wherein the pilot valve assembly includes means for sealing said rod relative to said pilot valve housing while permitting axial movement of the rod.

6. A thermally actuated valve assembly adapted for removable installation in a fluid flow path comprising a housing having a passage therein constituting a portion of said fluid flow path, said passage including an inlet, an outlet, and a valve seat between said inlet and said outlet, said valve assembly further comprising a valve member movable between a closed position in engagement with said valve seat for blocking the flow of fluid therethrough and an open position clear of the valve seat, a spring biasing the valve member toward its closed position, a thermostatic disk movable over center from a first curvature position to a second curvature position when subjected to a predetermined elevated ambient temperature level, means interconnecting said valve member and said disk, and abutment means carried by the housing and spaced from said disk when the latter is in'its first curvature position and engageable by said disk as it moves from its first to its second curvature position thereby to permit free movement of the disk until it engages said abutment means without application of force to said pilot valve member and, upon engagement of said disk with said abutment means, to apply a force to said valve member to move it against the force of the spring toward its open position. 

1. In a main valve assembly, such as for a fire extinguishing sprinkler, having a valve body with a main passage therethrough, one end of said main passage constituting an inlet adapted for connection to a pressurized fluid source and the other end thereof constituting an outlet adapted for the discharge of fluid, a main valve seat in said main passage between said inlet and said outlet, valve means movable between a closed position in engagement with said main valve seat blocking communication between said inlet and said outlet and an open position permitting the flow of fluid through said main passage, said main valve means having a first pressure area against which fluid pressure acts to move said valve means from its closed position to its open position and a second pressure area larger than the first pressure area against which fluid pressure acts to seat said valve means against said main valve seat so as to maintain said main valve means in its closed position against the force exerted by fluid pressure acting against said first pressure area, an auxiliary passage between said first pressure area and said second pressure area for equalizing fluid pressure applied to the first and second pressure areas, said auxiliary passage including a vent for venting fluid pressure from acting against said second pressure area; a thermally actuated pilot valve assembly for effecting opening of said main valve assembly in response to being subjected to a predetermined elevated ambient temperature, said pilot valve comprising a housing removably insertable as a unit into said valve body in said auxiliary passage between said second pressure area and said vent, a pilot valve passage in said valve housing consituting a portion of said auxiliary passage through which all fluid vented from said vent port must flow, said pilot valve passage having an inlet, an outlet and a valve seat therebetween, said pilot valve assembly further comprising a pilot valve member movable in said pilot valve housing between a closed position in which said pilot valve member is seated in said pilot valve thereby to block communication between said second pressure area in said vent so as to maintain fluid pressure acting against said second pressure area and to maintain said main valve means in its closed position and an open position for venting fluid pressure from said auxiliary passage thus reducing the fluid pressure acting against the second pressure area so as to enable fluid pressure acting against the first pressure area to open said main valve means, means for biasing said pilot valve towards its closed position, a thermostatic disk carried by said pilot valve housing, said disk being abruptly movable over center from a first curvature position to a second curvature position when subjected to said predetermined ambient temperature, means interconnecting said disk and said pilot valve member, and abutment means spaced from said disk when the latter is in its first curvature position and engageable by said disk as it moves From its first to its second curvature position thereby to permit free movement of said disk until it engages said abutment means without application of force to said pilot valve member and, upon engagement of the disk by said abutment means, to apply a force to said pilot valve member via said interconnecting means so as to move it against the force of said biasing means toward its open position.
 2. In a main valve assembly as set forth in claim 1 wherein said disk is reversibly movable from its second to its first curvature position upon its temperature falling below a second temperature less than said first predetermined temperature, said interconnecting means including means mounting said disk for varying the position of said disk relative to said abutment means whereby the disk may be calibrated to move from its second to its first curvature position at a preselected second temperature.
 3. In a main valve assembly as set forth in claim 1 wherein said interconnecting means is a rod interconnecting said disk in said pilot valve member, and wherein said biasing means includes a compression spring biasing said pilot valve member into engagement with its respective said valve seat.
 4. In a main valve assembly as set forth in claim 3 wherein said rod has a threaded portion at its outer end, and said interconnecting means comprises a nut adjustable on said threaded portion, said disk being carried by said nut so as to permit the disk to move freely between its first and second curvature positions, said disk being positioned on said rod so that said disk is clear of said abutment means when said pilot valve member is closed, and said disk is engageable with said abutment means only as said disk abruptly moves from its first to its second curvature position thereby to maintain said pilot valve member closed until said disk moves from its first to its second curvature position.
 5. In a sprinkler valve assembly as set forth in claim 4 wherein the pilot valve assembly includes means for sealing said rod relative to said pilot valve housing while permitting axial movement of the rod.
 6. A thermally actuated valve assembly adapted for removable installation in a fluid flow path comprising a housing having a passage therein constituting a portion of said fluid flow path, said passage including an inlet, an outlet, and a valve seat between said inlet and said outlet, said valve assembly further comprising a valve member movable between a closed position in engagement with said valve seat for blocking the flow of fluid therethrough and an open position clear of the valve seat, a spring biasing the valve member toward its closed position, a thermostatic disk movable over center from a first curvature position to a second curvature position when subjected to a predetermined elevated ambient temperature level, means interconnecting said valve member and said disk, and abutment means carried by the housing and spaced from said disk when the latter is in its first curvature position and engageable by said disk as it moves from its first to its second curvature position thereby to permit free movement of the disk until it engages said abutment means without application of force to said pilot valve member and, upon engagement of said disk with said abutment means, to apply a force to said valve member to move it against the force of the spring toward its open position. 